I. Field of the Invention
The present invention relates to a filter and, in particular, to a balance filter.
II. Description of the Prior Art
Recently, the portable electronic and mobile communication products have gradually become lighter, thinner, smaller-sized, more multi-functional, more reliable and cheaper. There is a tendency to develop high-density devices. The active and passive devices have become smaller-sized, integrated, on-chip and in-module to reduce the costs and improve the competitiveness of the devices.
There are some technologies, such as MLCC (multi-layer ceramic capacitor), via-drilling and via-filling of a single-layer substrate or lithography process, to shrink the size of a device by maximizing the usage of the space within the device. Conventionally, please refer to FIG. 1, via-drilling and via-filling 2 can be performed in a single-layer ceramic substrate 1. Then, multiple single-layer ceramic substrates 1 can be combined into a multi-layer substrate 3 (by sintering) to form a through-hole via 4 in a multi-layer ceramic substrate. A through-hole via 4 is used to electrically connect two adjacent conductive layers. The above-mentioned through-hole via is only used for an electrical connection between different layers, and the space of the through-hole via will require a larger substrate for accommodating it. Therefore, what is needed is a solution to fully utilize the space of a through-hole via to further shrink the size of a device and to achieve better electrical performance of the device.